1. Field of the Invention
This invention relates to a method for delivering a predetermined amount of a fluid wherein the fluid is pressurized and passed through a pressure feed passageway, the pressure feed passageway is opened and closed, and a predetermined amount of the fluid is thereby delivered out of the pressure feed passageway. This invention also relates to an apparatus for carrying out the method.
2. Description of the Prior Art
One of conventional apparatuses for delivering a predetermined amount of a fluid is disclosed in, for example, Japanese Unexamined Utility Model Publication No. 56(1981)-92817. With the disclosed apparatus, a piston is moved vertically in order to deliver a fluid out of a needle and to stop delivering the fluid.
However, with the disclosed apparatus for delivering a predetermined amount of a fluid, when the piston stops delivering the fluid out of the needle, the portion of the fluid, which is present in a fluid outlet part of the needle, flows back to a fluid reservoir region, which is located above the needle. As the portion of the fluid thus flows from the fluid outlet part of the needle back to the fluid reservoir region, air is sucked into the fluid outlet part of the needle. Specifically, the volume of the fluid pushing edge part of the piston, which is located in the fluid reservoir region, changes as the piston moves vertically in order to deliver the fluid and to stop delivering the fluid. When the piston stops delivering the fluid, the volume of the fluid pushing edge part of the piston, which is located in the fluid reservoir region, becomes smaller than when the piston works to deliver the fluid. As a result, when the piston stops delivering the fluid, the pressure in the fluid reservoir region becomes negative, and the portion of the fluid, which is present in the fluid outlet part of the needle, flows back to the fluid reservoir region. Therefore, air is sucked into the fluid outlet part of the needle.
Because the portion of the fluid, which is present in the fluid outlet part of the needle, flows back to the fluid reservoir region when the piston stops delivering the fluid, the portion of the fluid can be prevented from undesirably falling from the fluid outlet of the needle when the piston stops delivering the fluid. However, as described above, air is sucked into the fluid outlet part of the needle. Therefore, the problem occurs in that, when the fluid is thereafter delivered from the fluid outlet part of the needle, air thus sucked thereinto gets mixed with the fluid.
By way of example, in cases where the fluid which is to be delivered is a liquid adhesive, if air gets mixed with the adhesive, the problems described below occur. Specifically, when the adhesive containing air is delivered and applied to a material which is to be adhered, bubbles occur in the adhesive layer thus applied. Therefore, the adhesion strength becomes low at parts in the vicinity of the bubbles. Also, in cases where the material to be adhered is flexible, the material which has been adhered by the adhesive containing bubbles will get distorted at parts in the vicinity of the bubbles.